KENNEDY SPACE CENTER, FLA. - A worker in the Orbiter Processing Facility signals the crane operator to lower the Remote Manipulator System (RMS), or Shuttle arm, into place in Atlantis? payload bay. The RMS includes the electromechanical arm that maneuvers a payload from the payload bay of the orbiter to its deployment position and then releases it. It can also grapple a free-flying payload, maneuver it to the payload bay of the orbiter and berth it in the orbiter. The RMS arm is 50 feet 3 inches long and 15 inches in diameter. It weighs 905 pounds, and the total system weighs 994 pounds. The RMS has six joints that correspond roughly to the joints of the human arm, with shoulder yaw and pitch joints; an elbow pitch joint; and wrist pitch, yaw and roll joints. The end effector is the unit at the end of the wrist that actually grabs, or grapples, the payload. Atlantis is the designated orbiter to fly on mission STS-121. The mission has a launch window of July 12 - July 31, 2005.